sounds like broken door in the HVAC box, does air come out any vent? floor? defrost?

 

It blows out the other vents when it is in normal use and working good, but just shuts down the vents when it goes out, there still a tiny amount of air that comes out of them, but not near enough to make a difference.

 

I really dont know how much it comes out the floor or defrost when in normal use, because i never run those vents

 

That seems weird, all the vent doors are motorized so you would think if it works at one point while driving that it would work the same all the time. All of mine broke this last winter which really sucked having no heat, mine defaulted to cold air and dash vents that blow directly at you. I used the heater treaters to repair mine, I think there is another vendor called blend door usa. I didn't like the idea of having to cut into the heater box, but after I read what all was involved to remove the whole vent assembly, I decided to go this route. There were several youtube videos I found showing how to do this and it was easier that I thought. When I finished, everything works again.

Not sure if this is what is wrong with yours having it work sometimes and not others, but this is a common problem in these trucks, so just something to consider.

 

Evaporator freezing at highway speed, my guess:wink2:

 

Mine did this years ago, was low on refrigerant.

 

Make sure have the correct refrigerant level.
Monitor high side and low side pressure for further diagnostic.

 

Ok, thanks, I will check the refrigerant level, I hope that is the problem